Effects of large doses of estrogen on prolactin and growth hormone release.

The effects of large doses of estrogen on prolactin (PRL) release were assessed. Circulating PRL levels in response to intravenous infusion of 17 beta-estradiol (E2), at a rate of 50 mug per hour for 4 hours, were studied in 10 subjects, and a chronic administration of ethinyl estradiol (EE) at a dose of 400 mug per day, for 1 week, was evaluated in five hypogonadal subjects. There was a significant depression of serum level of PRL during the E2 infusion and a significant increase in PRL release after discontinuation of the infusion. The chronic treatment of large doses of EE induced a more rapid (within 36 hours) and a significantly greater elevation of PRL levels at the end of 1 week treatment than those found during smaller doses of EE administration, as reported previously. These data suggest that acute treatment of estrogen may have a biphasic action on the pituitary PRL section and that the augmentatory effect of estrogen on PRL secretion is dose-dependent in human beings.